| Titanium dioxide is an important inorganic chemical material, which has extensively used in white pigment, paper, plastics, rubbers, porcelain, and fibers, etc. In Industry, the raw materials of titanium dioxide are sea sand, ilmenite, magnetite and high titanium slag.Ilmenite is smelted to produce the titanium slag, and the TiO2content is increased. The titanium slag which contains more than90%TiO2is used as the raw materials of chloride process, while the titanium slag with TiO2concentration lower than90%can be treated as the quality materials of sulfate process.With the enhancement of environmental protection consciousness of people, the development of circular economy and construction of environment-friendly society are the special direction that we want to consider. In this paper, the titanium slag from Sichuan Province is adopted as the raw materials. The process for titanium dioxide production was proposed by roasting the titanium slag with concentrated sulfuric acid or ammonium bisulfate. Results are as follows:1) The effects of mass ratio of acid to ore, roasting temperature, roasting time, and material particle size on the acidolysis rate of titanium slag through roasting with concentrated sulfuric acid were investigated. The results of orthogonal experiments based on the single factor experiments showed that the optimum technological conditions were obtained as mass ratio of acid to ore of2.1:1, roasting temperature of310℃, roasting time of75min and material particle size of45-53μm. The extracting rate of TiO2was about96%under the optimum conditions. The roasting kinetics of titanium slag with concentrated sulfuric acid is investigated by the un-reaction shrinking core model, the results showed that the reaction rate is controlled by the internal diffusion on the solid product layer. According to the Arrhenius expression, the apparent activation energy of the roasting reaction is18.94kJ·mol-1and the kinetics model can be expressed as:1+2(1-x)-3(1-x)2/3=0.49exp[-18940/R]-t5.2) The effects of mass ratio of water-to-solid, dissolving temperature, stirring speed and dissolving time on the dissolving rate of roasted titanium slag by concentrated sulfuric acid were investigated. The optimum technological conditions through the single factor experiments is as follows:mass ratio of water-to-solid5:1, dissolving temperature60℃, stirring speed400r-min-1and dissolving time40min. The dissolving rate of TiO2was about96%under the optimum conditions. The dissolving kinetics was investigated by the un-reaction shrinking core model, the results showed that the internal diffusion on the solid product layer is the rate-controlling step. According to the Arrhenius expression, the apparent activation energy for the dissolving reaction is39.58kJ-mol-1and the kinetics model can be expressed as:1+2(1-x)-3(1-x)2/3=2.86x103exp[-39584/RT]·t.3) The effects of mass ratio of ammonium bisulfate to ore, roasting temperature, roasting time and material particle size on the extracting rate of TiO2were investigated. The results of orthogonal experiments based on the single factor experiments showed that the optimum technological conditions were obtained as mass ratio of ammonium bisulfate to ore of4:1, roasting temperature of480℃, roasting time of60min and material particle size of45～53μm. The extracting rate of TiO2was about85%under the optimum conditions. The reaction kinetics of roasting titanium slag with ammonium bisulfate was studied. The experimental data of the extracting rate of titanium dioxide showed that the roasting process can be modeled with the un-reaction shrinking core model and the reaction rate is controlled by chemical reaction. According to the Arrhenius expression, the apparent activation energy of the roasting reaction is87.95kJ-mol-1and the kinetics model can be expressed as:1-(1-x)1/3=8.14x103exp[-87945/RT]·t.4) The effects of mass ratio of water-to-solid, dissolving temperature, stirring speed and dissolving time on the dissolving rate of the roasted titanium slag were investigated. The results of experiments based on the single factor experiments showed that the optimum technological conditions were obtained as mass ratio of water-to-solid of5:1, dissolving temperature of70℃, stirring speed of500r·min-1and dissolving time of50min. The dissolving rate of TiO2was about95%under the optimum conditions. The dissolving kinetics was investigated with the un-reaction shrinking core model, the results showed that the reaction rate is controlled by the internal diffusion on the solid product layer. According to the Arrhenius expression, the apparent activation energy for the dissolving reaction is39.80kJ-mool-1and the kinetics model can be expressed as:1+2(1-x)-3(1-x)2/3=13.30×l03exp[-39797/R7]·t.5) The effects of bottom water volume, hydrolysis temperature, feed fluid rate and hydrolysis time on the hydrolysis rate of titanium sulfate solution were investigated. The optimum operating conditions based on the single factor experiments were obtained as bottom water volume of67mL(6:1), hydrolysis temperature of100℃, feed fluid rate of40ml-min’1and hydrolysis time of90min. The hydrolysis rate was about95%under the optimum conditions.6) The product of Al2O3was obtained from the solution precipitated titanium. The effects of reaction temperature, pH and reaction time on the aluminium precipitation rate were investigated. The optimum operating conditions through the single factor experiments comprises reaction temperature of60℃, precipitation pH of6and reaction time of20min. The aluminium precipitation rate was about99%under the optimum conditions; the optimum conditions of alkali dissolution of aluminium hydroxide were obtained as reaction temperature of70℃, mass ratio of aluminium hydroxide to alkali of1:4, reaction time of30min. The dissolution rate of aluminium hydroxide was about100%under the conditions; the optimum operating conditions on the carbonation were obtained as CO2gas flow rate30-40ml-min-1under normal atmospheric pressure and temperature, the pH end point for carbonation is8. The aluminium reaction rate was98%.7) The effects of mass ratio of sodium hydroxide to the residue, reaction temperature, reaction time and liquid-solid ratio on the extracting rate of SiO2were investigated in the process of extracting silicon from the residue by sodium hydroxide. The optimum operating conditions through the single factor experiments were obtained as reaction temperature of190℃, mass ratio of sodium hydroxide to the residue of3:1, liquid-solid ratio of4.5:1and reaction time of60min. The extracting rate of SiO2was about74.09%, and the sodium silicate solution was processed by calcification. The optimum operating technology through the single factor experiments was established: the mol ratio of CaO to Na2SiO31:1, reaction temperature100℃, reaction time45min. The calcification rate of sodium silicate solution was over94%. |
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